Phenoxymethyloxiranes, for example 2-(4-nitrophenoxymethyl)-oxirane, and phenyloxiranecarboxylic acid esters, for example 2-phenyloxirane-2-carboxylic acid ethyl ester, inter alia, are within the scope of an investigation into the ability of substituted cyclic compounds (with a three-membered ring) to serve as a substrate or inhibitor for epoxide hydrase from guinea pig liver microsomes [F. Oesch et al., Biochem., 10 (1971) No. 26, 4,858-66]. Phenalkoxyalkyl- and phenoxyalkyl-substituted oxiranecarboxylic acids have now been found to be pharmaceutically-active compounds with a specific action.